The question mark [ ? ] (also known as interrogation point, query, or eroteme in journalism)[1] is a punctuation mark that indicates an interrogative clause or phrase in many languages. The question mark is not used for indirect questions. The question mark glyph is also often used in place of missing or unknown data. In Unicode, it is encoded at U+003F?QUESTION MARK (HTML &#63;).

This earliest question mark was a decoration of one of these dots, with the "lightning flash" perhaps meant to denote intonation, and perhaps associated with early musical notation like neumes. Another possibility is that it was originally a tilde or titlo, as in " ·~ ", one of many wavy or more or less slanted marks used in medieval texts for denoting things such as abbreviations, which would later become various diacritics or ligatures.[4][5] Over the next three centuries this pitch-defining element (if it ever existed) seems to have been forgotten, so that the Alcuinesque stroke-over-dot sign (with the stroke sometimes slightly curved) is often seen indifferently at the end of clauses, whether they embody a question or not.

In the early 13th century, when the growth of communities of scholars (universities) in Paris and other major cities led to an expansion and streamlining of the book-production trade,[6] punctuation was rationalized by assigning Alcuin's stroke-over-dot specifically to interrogatives; by this time the stroke was more sharply curved and can easily be recognized as the modern question mark.

It has also been suggested that the glyph derives from the Latinquaestiō meaning "question", which was abbreviated during the Middle Ages to qo.[7] The lowercase q was written above the lowercase o, and this mark was transformed into the modern symbol. However, evidence of the actual use of the Q-over-o notation in medieval manuscripts is lacking; if anything, medieval forms of the upper component seem to be evolving towards the q-shape rather than away from it.[citation needed]

One possible origin of the question mark from Latin

According to a 2011 discovery by a Cambridge manuscript expert, Syriac was the first language to use a punctuation mark to indicate an interrogative sentence. The Syriac question mark has the form of a vertical double dot.[8]

In English, the question mark typically occurs at the end of a sentence, where it replaces the full stop (period). However, the question mark may also occur at the end of a clause or phrase, where it replaces the comma (see also question comma):

Is it good in form? style? meaning?

or:

"Showing off for him, for all of them, not out of hubris—hubris? him? what did he have to be hubrid about?—but from mood and nervousness." — Stanley Elkin.[9]

This is quite common in Spanish, where the use of bracketing question marks explicitly indicates the scope of interrogation.

En el caso de que no puedas ir con ellos, ¿quieres ir con nosotros? ('In case you cannot go with them, would you like to go with us?')

A question mark may also appear immediately after questionable data, such as dates:

In Spanish, since the second edition of the Ortografía of the Real Academia Española in 1754, interrogatives require both opening (¿) and closing (?) question marks.[10][11] An interrogative sentence, clause, or phrase begins with an inverted question mark (¿) and ends with the question mark (?), as in:

Ella me pregunta «¿qué hora es?» – 'She asks me, "What time is it?"'

Question marks must always be matched, but to mark uncertainty rather than actual interrogation omitting the opening one is allowed, although discouraged:[12]

Catalan and Galician also use the inverted opening question mark, though usually only in long sentences or in cases that would otherwise be ambiguous. Basque only uses the terminal question mark.[clarification needed]

The Greek question mark (Greek: ερωτηματικό, translit.erōtīmatikó) looks like ";". It appeared around the same time as the Latin one, in the 8th century.[14] It was adopted by Church Slavonic and eventually settled on a form essentially similar to the Latin semicolon. In Unicode, it is separately encoded as U+037E;GREEK QUESTION MARK, but the similarity is so great that the code point canonically decomposes as equivalent to U+003B;SEMICOLON, making the marks identical in practice.[15]

In Arabic and other languages that use Arabic script such as Persian and Urdu, which are written from right to left, the question mark ؟ is mirrored right-to-left from the English question mark. In Unicode, two encodings are available: U+061F؟ARABIC QUESTION MARK (HTML &#1567;· With bi-directional code AL: Right-to-Left Arabic) and U+2E2E⸮REVERSED QUESTION MARK (HTML &#11822;· With bi-directional code Other Neutrals). (Some browsers may display the character in the previous sentence as a forward question mark due to font or text directionality issues).

The Arabic question mark is also used in some other right to left scripts: Thaana, N'Ko, and Syriac.

Hebrew and Yiddish are also written right-to-left, but they use a question mark that appears on the page in the same orientation as the Roman-alphabet question mark.[16]

The question mark is also used in modern writing in Chinese and Japanese, although it is not strictly necessary in either. Usually it is written as fullwidth form in Chinese and Japanese, in Unicode: U+FF1F？FULLWIDTH QUESTION MARK (HTML &#65311;).[clarification needed]

French usage must include a narrow non-breaking space before the question mark (for example, "Que voulez-vous boire ?"),[17] whereas in the English language orthography no space is allowed in front of the question mark (e.g. "What would you like to drink?"). See also: Plenken.

In typography, some stylistic variants and combinations are available:

The rhetorical question mark or percontation point was invented by Henry Denham in the 1580s and was used at the end of a rhetorical question; however, its use died out in the 17th century. It was later revived in modern-day society by Matt DiRoberto. It was the reverse of an ordinary question mark, so that instead of the main opening pointing back into the sentence, it opened away from it.[18] This character can be represented using the reversed question mark (⸮) found in Unicode as U+2E2E. The percontation point is analogous to the irony mark, but those are even more rarely seen.

Bracketed question marks can be used for rhetorical questions, for example Oh, really(?), in informal contexts such as closed captioning. For an ironic or sarcastic statement, a bracketed exclamation mark may be used: Oh, really(!).

The question mark can also be used as a meta-sign to signal uncertainty regarding what precedes it. It is usually put between brackets: (?). The uncertainty may concern either a superficial level (such as unsure spelling), or a deeper truth (real meaning).

In computing, the question mark character is represented by ASCII code 63 (0x3F hexadecimal), and is located at Unicode code-point U+003F?QUESTION MARK (HTML &#63;). The full-width (double-byte) equivalent (？), is located at code-point U+FF1F？FULLWIDTH QUESTION MARK (HTML &#65311;).[19]

The question mark is often utilized as a wildcard character: a symbol that can be used to substitute for any other character or characters in a string. In particular "?" is used as a substitute for any one character as opposed to the asterisk, "*", which can be used as a substitute for zero or more characters in a string. The inverted question mark (¿) corresponds to Unicode code-point U+00BF¿INVERTED QUESTION MARK (HTML &#191;·&iquest;), and can be accessed from the keyboard in Microsoft Windows on the default US layout by holding down the Alt and typing either 1 6 8 (ANSI) or 0 1 9 1 (Unicode) on the numeric keypad. In GNOME applications on GNU Linux operating systems, it can be entered by typing the hexadecimal Unicode character (minus leading zeros) while holding down both Ctrl and Shift, I J mm.e.: Ctrl Shift B F. In recent XFree86 and X.Org incarnations of the X Window System, it can be accessed as a compose sequence of two straight question marks, i.e. pressing Compose ? ? yields ¿. In classic Mac OS and Mac OS X (macOS), the key combination Option Shift ? produces an inverted question mark.

The question mark is used in ASCII renderings of the International Phonetic Alphabet, such as SAMPA, in place of the glottal stop symbol, ʔ, (which resembles "?" without the dot), and corresponds to Unicode code point U+0294ʔLATIN LETTER GLOTTAL STOP (HTML &#660;).

In computer programming, the symbol "?" has a special meaning in many programming languages. In C-descended languages, ? is part of the ?: operator, which is used to evaluate simple boolean conditions. In C# 2.0, the ? modifier is used to handle nullable data types and ?? is the null coalescing operator. In the POSIX syntax for regular expressions, such as that used in Perl and Python, ? stands for "zero or one instance of the previous subexpression", i.e. an optional element. In certain implementations of the BASIC programming language, the ? character may be used as a shorthand for the "print" function; in others (notably the BBC BASIC family), ? is used to address a single-byte memory location. In OCaml, the question mark precedes the label for an optional parameter. In Scheme, as a convention, symbol names ending in ? are used for predicates, such as odd?, null?, and eq?. Similarly, in Ruby, method names ending in ? are used for predicates. In Swift, a type followed by ? denotes an option type; ? is also used in "optional chaining", where if an option value is nil, it ignores the following operations.

In many Web browsers and other computer programs, when converting text between encodings, it may not be possible to map some characters into the target character set. In this situation it is common to replace each unmappable character with a question mark ?, inverted question mark ¿, or the Unicode replacement character, usually rendered as a white question mark in a black diamond: U+FFFD�REPLACEMENT CHARACTER. This commonly occurs for apostrophes and quotation marks when they are written with software that uses its own proprietary non-standard code for these characters, such as Microsoft Office's "smart quotes".

The generic URL syntax allows for a query string to be appended to a resource location in a Web address so that additional information can be passed to a script; the query mark, ?, is used to indicate the start of a query string. A query string is usually made up of a number of different field/value pairs, each separated by the ampersand symbol, &, as seen in this URL:

http://www.example.com/search.php?query=testing&database=English

Here, a script on the page search.php on the server www.example.com is to provide a response to the query string containing the pairs query=testing and database=English.

A question mark is used in English medical notes to suggest a possible diagnosis. It facilitates the recording of a doctor's impressions regarding a patient's symptoms and signs. For example, for a patient presenting with left lower abdominal pain, a differential diagnosis might include ?diverticulitis (read as "query diverticulitis").